“Maybe grandma’s secret family recipe isn’t so secret after all.”

Atlas Obscura: The Dirty Secret of ‘Secret Family Recipes’. “Surprisingly often, they’re copied from mayo jars and famous cookbooks.”

“When Danny Meyer was gearing up to open his barbecue restaurant, Blue Smoke, there was one recipe he knew he had to have on the menu: his grandmother’s secret potato salad recipe.

“I told the chef, ‘My very favorite potato salad in the world was the one my grandmother made,’“ Meyer recalls.
When Meyer arrived, the sous chefs had a big bowl of potato salad that brought back memories of his grandmother. He tried it, smiled, and told the chefs, “That’s exactly right.“ They grinned back at him mischievously. Eventually, Meyer broke and asked, “What’s so funny?“ A chef pulled out a jar of Hellman’s mayonnaise and placed it on the table. Meyer looked at it, then realized that the secret recipe his grandmother had hoarded for years was on the jar. It was the official Hellman’s recipe for potato salad.”

Even more enjoyable to read is the MetaFilter posting from which this link came. Members share their not-so-secret family recipes.